MRI Principles (Advanced)
description
Transcript of MRI Principles (Advanced)
-
MRI Principles
Wen-Yang Chiang
Oct 13, 2007
-
http://www.mrisprostatecancercenter.com/
dr-wheeler_the_prostate_center_hifu.html
http://www.med.umich.edu/opm/newspage/2004/b
raintumor.htm
Diffusion
Tractography
MRS
HIFU
Functional
MRI
-
Magnetic Resonance Imaging
Nuclear spinning
generates micro magnet
The alignment of nuclear
spin using external
magnetic field Apply RF pulse which is
close to Larmor frequency
Resonance
Transform the received
signal to image
MRI
Nuclear process within
external magnetic field
0B Provide spatial
information
-
www.e-mri.org
Basic Physics
-
Nuclear Spin
www.e-mri.org
Basic Physics
-
Processing & Larmor Frequency
00 B www.e-mri.org
Basic Physics
-
Net Magnetization
www.e-mri.org
Basic Physics
-
Excitation & Relaxation
www.e-mri.org
Signal
Formation
-
90 Pulse
www.e-mri.org
Signal
Formation
-
180 Pulse after 90 Pulse
www.e-mri.org
Signal
Formation
-
180 Pulse
www.e-mri.org
Signal
Formation
-
Relaxation
www.e-mri.org
Signal
Formation
-
Slice Selection
www.e-mri.org
Signal
Formation
-
Slice Selection
www.e-mri.org
Signal
Formation
-
Frequency Encoding
www.e-mri.org
Signal
Formation
-
Frequency Encoding
www.e-mri.org
Signal
Formation
-
Phase Encoding
www.e-mri.org
Signal
Formation
-
Phase Encoding
www.e-mri.org
Signal
Formation
-
Spatial Encoding
dx
dBg
B
x
Different g or t
dxextgS txgj )(),(
Signal Interpretation
-
Sinusoidal Encoding
greater gradient or longer t => higher frequency encoding
Signal Interpretation
-
xB(x) = gx xB
Spatial Encoding
AB
C
+ +=
A
B
C
Signal Interpretation
-
Sinusoidal Modulation
x
y
x-dir gradient
y-dir gradient
2D sinusoidal wave function
),(
,)(),(
yxv
vdevtgS tvgj
Signal Interpretation
-
MRI Reconstruction
Superposition of sinusoidal functions
tgk
yxv
kdekSv vkj
),(
,)(2
1)(
Image Formation
-
Contrast
Image Formation
-
Contrast
www.e-mri.org
Image Formation
-
Spin Echo Sequence
gz
gy
gx
RF
90 180 echo
kx
kyTR
90
TE/2
Scan time = TR x # ky lines x NEX
FID Spin Echo
-
K-Space & Image Space
-
kx
ky
Kmax = Kmax/2Kmax
-
Blurring
-
kx
ky
Kmax
k = 2 k
-
Aliasing
-
This is just the
beginning